September 11, 2012

The plant itself is called Pollia condensata, and researchers have now explained the material magic underlying its marvelous hues: layers of cells that refract light in a manner usually seen in butterfly wings and beetle shells.

"Structural colors come about not by pigments that absorb light, but the way transparent material is arranged on the surface of a substance"....

It tends to be blues, at least in birds. The microscopic structures on the feathers are small enough to interfere with light waves, contructively reflecting the blue end of the spectrum and absorbing the red end.

I don't follow the article on circularly polarized light. You can see it just fine.

A quarter wave plate will convert linear to circular and vice versa.

A polarized stereo projectionist will drop a quarter wave plate in front of the projector so that the audience (with linear glasses) sees both images in both eyes while he adjusts the projector. He himself drops a quarter wave plate over his own glasses and sees the stereo images, left circular in one eye and right circular in the other. When it's all adjusted, he removes the quarter wave plate and everything is linear again for the audience.

The conversion to circular happens when two axes of the medium have a different indices of refraction for two aligned linear polarizations. A linear (unaligned) mixture in then produces circular out, for the right thickness of the medium.

The rainbow of colors you see due to a drop of oil floating on water is the result of 'structural color' (an odd term I'd never heard before; maybe the author thought 'interference' was too confusing.)For that matter, a rainbow itself is due to structural color, but caused by refraction rather than interference.